1. Field of the Invention
The present invention relates to a hot stamping mold. More particularly, the present invention relates to a hot stamping mold having both a high strength unit and a low strength unit to produce formed goods.
2. Description of Related Art
Typically, efforts have been made to improve both a reduction in weight and collision safety of a vehicle body in a vehicle industry.
Recently, as shown in FIG. 1, a hot stamping technology that is a hot press forming technology using a steel sheet 111 (particularly, boron steel sheet) has been actively researched in order to satisfy both hardness and a reduction in weight of a steel sheet material.
That is, the hot stamping technology is a forming technology of heating the steel sheet 111 to an appropriate temperature to perform forming in a press mold 113 using press forming at a time and then performing quenching to manufacture high strength parts 115.
Accordingly, hot stamping formed goods may have strength that is four or five times higher than that of typical steel sheet parts and a weight reduced by 40% at most as compared to the typical steel sheet parts. Therefore, as described above, there is a merit in that both the reduction in weight and strength of the vehicle body can be improved.
Meanwhile, recently, formed goods having both a high strength unit and a low strength unit with a transition segment interposed therebetween have been produced by partially heating a steel sheet in a mold to perform forming.
As described above, the hot stamping forming technology enabling the formed goods to have both the high strength unit and the low strength unit may satisfy the reduction in weight of the vehicle body and partially secure both collision absorption performance and hardness to improve safety.
An example of application of the hot stamping forming technology may include a center filler 100 of the vehicle body shown in FIG. 2.
That is, in the case of the center filler 100, it is ideal that a bottom unit directly receiving an effect of collision be formed of a low strength unit L to improve collision absorption performance and a top unit slightly receiving an effect of direct collision be formed of a high strength unit H so as to maintain an entire frame of the vehicle body, thus improving hardness.
As described above, the formed goods having both the high strength unit H and the low strength unit L are partially heated in the mold. Accordingly, there are drawbacks in that the transition segment TS between the high strength unit H and the low strength unit L is widely distributed and a position of the transition segment TS is not uniform due to adiabatic inferiority of the mold and thermal expansion of the mold.
The drawbacks make it difficult to satisfy design specs of segments of the high strength unit H and the low strength unit L of the formed goods and to minimize the transition segment TS.
Further, there is a drawback in that dimensional precision of the formed goods is poor due to thermal expansion of the mold.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.